1. Field of the Invention
The present invention relates to a web transport device for transporting a continuous web such as a film or a tape wound on a rotary member to another rotary member in an automatic manner, and more particularly such web transport device capable of controlling the web transport when the web wound on the rotary member at the unwinding side is near its the end.
2. Description of the Prior Art
In a conventional web transport device for transporting a continuous web such as film wound on an unwinding rotary member to another winding rotary member such as a reel by driving said winding rotary member, there may result a web breakage, a failure in the driving system, an overheating of the motor if the web is fixed at the trailing end thereof on the unwinding rotary member and is transported at a high speed to said trailing end. On the other hand, if said trailing end is not fixed on the unwinding rotary member, the trailing end often becomes detached from the unwinding rotary member and the entire web is eventually transferred onto the winding rotary member, so that said trailing end has to be fixed again on said unwinding rotary member in case the web is to be returned to said unwinding rotary member.
In order to overcome such inconvenience, there has been proposed a method of attaching a special mark on the web in the vicinity of said trailing end and providing detecting means such as a microswitch for detecting said mark, wherein the web transport is terminated when said detecting means detects said mark on the web.
Such method however leads to an increased production cost because of an additional manufacturing step for attaching said special mark to the web and of the use of additional detecting means, and requires the use of a long trailer tape at the end of the web since said mark has to be positioned considerably in front of the web end in consideration of the time required from the mark detection to the web stopping. Also the web is often damaged by said detecting means, which is in most cases composed of mechanical means such as a microswitch achieving said mark detection through contact with the web. Furthermore said method is not applicable to a web not provided with said mark.